This invention relates generally to non-mechanical micropumps, and more particularly, to electroosmotic micropumps fabricated using microfabrication techniques.
Various types of micropumps have been fabricated using microfabrication techniques. Micropumps can be classified into two categories: mechanical and non-mechanical. Mechanical micropumps such as electrostatically driven reciprocating pumps and thermopneumatically driven peristaltic pumps, contain moving pumps which are of serious concern for long-term reliability. Some of the non-mechanical micropumps, such as electrohydrodynamic micropumps and magnetohydrodynamic, micropumps cannot pump deionized (DI) water due to their fundamental working principles. As a result, these types of non-mechanical micropumps have limited use in medical and biological applications.
A newer type of non-mechanical pump is the electrokinetic (EK) or electroosmotic (EO) pump, which uses electroosmotic flow in a porous media to generate pressures in excess of ten atmospheres (atm). The pressure capacity of EO pumps far exceeds the capacity of other types of micropumps. Electroosmotic pumps have the advantage of being compatible with aqueous solutions as the working fluid. This capability is essential for biological and medical applications. A disadvantage of EO pumps is the complexity of integrating porous media, e.g., packed silica particle beds, into microdevices.
Electroosmotic pumps generate fluid flow and pressure through the application of an electrical potential across a stationary, fluid-filled structure. EO pumps are among a family of devices that take advantage of the electric double layer that typically forms at a liquid-solid interface. Structures used for electroosmotic pumping must have pore-like features within a few orders of magnitude of the size of the electric double layer, which is generally less than a micron. Electroosmotic flit pumps produce high pressures and flow rates in high surface-to-volume structures with micron-sized pores. Electroosmotic frit pumps made from sintered glass frits have been reported that generate pressures of 250 kPa and flow rates of 10 mL/min.
There is a need for electroosmotic micropumps having high pressure and flow rate capacity that can be fabricated from planar structures, such as plastic, glass or silicon substrates, particularly where standard microfabrication techniques, such as microlithography and wet etching, can be used in fabrication. Such electroosmotic micropumps can be directly integrated onto microsystems.